1. Field of the Invention
The present invention relates to a semiconductor device including an insulated gate switching element, and more particularly relates to a semiconductor device including an overcurrent protection circuit to protect a switching element from an overcurrent.
2. Description of the Related Art
FIG. 12 shows a typical cross-sectional configuration of a lateral insulated gate bipolar transistor (hereinafter referred to as an “IGBT”) which is used as a high-voltage semiconductor switching element. As shown in FIG. 12, an N-type extended drain region 52 and a P-type base region 53 adjacent to the extended drain region 52 are formed in surface portions of a semiconductor substrate 51. An N+-type emitter region 54 is formed in a surface portion of the base region 53 so as to be spaced apart from the extended drain region 52. A gate insulating film 56 is formed on the base region 53 so as to extend on a part of the emitter region 54 and on a part of the extended drain region 52, and a gate electrode 57 is formed on the gate insulating film 56. A P-type collector region 58 is formed in a surface portion of the extended drain region 52 so as to be spaced apart from the base region 53.
Moreover, the IGBT shown in FIG. 12 includes a collector terminal P1′ electrically connected to the collector region 58, a gate terminal P2′ electrically connected to the gate electrode 57, and an emitter terminal P3′ electrically connected to the emitter region 54.
The lateral IGBT shown in FIG. 12 is turned on when a forward bias voltage is applied between the gate terminal P2′ and the emitter terminal P3′ with the collector terminal P1′ set to a high potential. Conversely, when a zero bias voltage or a reverse bias voltage is applied between the gate terminal P2′ and the emitter terminal P3′, the lateral IGBT is turned off. In this manner, the lateral IGBT has a switching characteristic in which the lateral IGBT is turned on and off in accordance with the gate voltage applied to the gate electrode 57.
A semiconductor device including such a lateral IGBT is often used with an inductive load connected between the collector terminal P1′ and a power supply. If a failure occurs in such a situation, the inductive load is short-circuited, causing a current more than several times a rated current to pass through the lateral IGBT. When the load is thus short-circuited, it is necessary to sense the overcurrent so as to interrupt the gate voltage or the collector voltage, because otherwise there would be a thermal breakdown in the lateral IGBT due to the temperature increase.
In view of this, a semiconductor device having an overcurrent protection function for lateral IGBT shown in FIG. 13 has been proposed (see Patent Document 1). The semiconductor device 10 shown in FIG. 13 includes a lateral IGBT 1, which is a principal switching element controlled by a gate voltage, and a current detection lateral IGBT 2 connected in parallel to the lateral IGBT 1. Respective gate electrodes of the lateral IGBTs are electrically connected to the gate terminal P2′, respective collector regions in the lateral IGBTs are electrically connected to the collector terminal P1′, and an emitter region in the lateral IGBT 1 as the principal switching element is electrically connected to the emitter terminal P3′. An emitter region in the current detection lateral IGBT 2 is connected with a sense resistor 23 as a current detection resistor. In the semiconductor device 10 shown in FIG. 13, a current detection circuit 20, which is electrically connected with the current detection lateral IGBT 2, includes a voltage comparator 21, a reference voltage circuit 22, and the aforementioned sense resistor 23, both of which are connected with the voltage comparator 21. The respective other ends of the reference voltage circuit 22 and the sense resistor 23 are electrically connected to the emitter terminal P3′.
In the semiconductor device 10 of FIG. 13, a current 9 passing through the current detection lateral IGBT 2 flows through the sense resistor 23 to the emitter terminal P3′. As a result, a voltage generated between both ends of the sense resistor 23 is compared with a voltage generated by the reference voltage circuit 22 by the voltage comparator 21, and a current 8 passing through the lateral IGBT 1 as the principal switching element is controlled based on the thus obtained voltage difference.
[Patent Document 1] Japanese Laid-Open Publication No. 9-260592
[Patent Document 2] Japanese Laid-Open Publication No. 7-297387